The invention relates to an electroacoustic transducer, in particular for use in an apparatus for medical shock-wave treatment, in which the transducer has a plurality of piezoelements arranged next to one another.
Such electroacoustic transducers are part of the state of the art and are used for example in lithotripters, such as for non-invasive treatment of stone problems. Medical shock-wave treatment apparatus meanwhile are very widespread in the medical field and are also applied for numerous other therapy purposes. Various physical principles are known for the production of shock waves. The subject matter of the present invention involves those apparatus which operate according to the piezoelectric principle, which means they have an electroacoustic transducer which is constructed from a multitude of piezoelements, also referred to as piezoelectric elements.
Such electroacoustic transducers are often designed as self-focussing transducer calottes. With such transducer calottes, a multitude of piezoelements are bonded in an electrically conductive manner, for example on a hemispherical metal calotte as a carrier, and are embedded into an elastic, electrically insulating cast mass of epoxy resin. The electrical connection of the piezoelements, which are to be connected in parallel, is thereby effected on the one hand via the metal calotte and on the other hand via a wiring on the other side of the piezoelements. Such a construction of an electroacoustic transducer is known for example from German published patent application DE 196 24 443 A1.
The electroacoustic transducer forms the core piece of the lithotripter. Since it requires much effort with regard to manufacture and is thus expensive, one strives to construct these transducers such that, apart from its good therapeutic characteristics, it also has a life duration as long as possible. The life duration of such an electroacoustic transducer functioning in a piezoelectric manner is typically limited by two causes, on the one hand by the high-voltage arc-overs at the piezoelement, which destroy the element within a short time and also damage adjacent elements as well as their insulation, and on the other hand by the fact that the piezoelements detach from the carrier calotte, which first leads to a reduction of the power, but with continued operation of the transducer leads to a fracture formation within the piezoelement and finally to a high-voltage arc-over.
While the high-voltage arc-overs due to faulty piezoelements occur practically independently of the operating time and tend rather to be the exception, detachment of the piezoelements from the carrier calotte is greatly dependent on the operating time of the transducer.
Although it is part of the state of the art from German published patent application DE 196 24 443 A1 to reduce the tendency for a high-voltage arc-over by a special insulation at the piezoelements, this however has no influence on the problem of detachment of the piezoelements from the carrier calotte.
The fastening of the piezoelements on the carrier calotte is known from German published patent applications DE 34 25 992 A1 and DE 33 19 871 A1. It is effected by an electrically conductive epoxide adhesive having a high silver component, by which the piezoelements are connected in an electrically conductive manner and mechanically to the metallic carrier calotte. It is indeed in this region, however, that the detachments occur with long-term loading.